Personal subscriber stations that each simultaneously access a plurality of frequency channels in mobile WiMax, particularly, WiBro (wireless broadband Internet) for data transmission and reception (hereinafter referred to as “multi-FA personal subscriber terminals”) have been developed.
In the related art, a technique of allocating a plurality of frequency channels to a specific terminal in a cell and a technique of performing hand-off from a bad frequency channel to a good frequency channel according to a wave propagation environment of a base station are disclosed.
According to the related art, in order to control errors in data, a HARQ (hybrid ARQ) function, which is a method of controlling errors by combining retransmission and error correction, is defined in a physical layer. A packet data service system that generates many packets, e.g., wireless Internet packets, in a short time, that is, that generates packet bursts, can improve a packet processing rate through error control using a HARQ method.
Further, in the related art, TCP (transmission control protocol) is generally used as one of core protocols for transmitting packet data.
As is known, the TCP protocol errorlessly transmits user data from end to end. In order for error correction, the receiving side transmits an ACK (acknowledge) for the received TCP segment. Further, if the transmitting side does not receive the ACK, it performs retransmission and congestion control.
In this case, the TCP transmits the ACK in a cumulative ACK manner. In the cumulative ACK manner, an ACK number represents a bite number of data in a data stream that is received and perceived by the receiving side. In other words, the ACK number represents the next octet number that the transmitting side should transmit.
The cumulative ACK manner should not perform retransmission even though an ACK packet is lost. Therefore, even though one ACK packet is lost during data transmission, all data having been received can be perceived through an ACK for the next data packet.
However, when a data packet is partially lost and then the next packet is received, or when a data packet is not received according to the sequence number of data packets, the receiving side cannot perceive the data packet. Therefore, the transmitting side is required to perform retransmission.
Therefore, in a portable Internet technique, if the HARQ is operated, or if one terminal simultaneously accesses two or more frequency channels for transmitting or receiving data packets, TCP packets are not transmitted according to the sequence number, resulting in decreased transmission efficiency.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.